The present invention relates to two-dimensional phased array ultrasound transducers and, more particularly, to a two-dimensional phased array ultrasound transducer with a convex environmental barrier for maximizing contact with a patient""s body.
Ultrasound systems offer a non-invasive means for medical personnel to monitor physiological activity within a patient""s body. Such a system includes an ultrasound transducer that is positioned against the patient""s body. The transducer transmits ultrasonic signals into the patient""s body, and receives echo signals that are then processed to provide an image of an internal organ. An acoustic gel is placed between the transducer and the patient""s body to improve acoustic coupling of the ultrasonic signals.
Ultrasound transducers are categorized as either one-dimensional phased arrays or two-dimensional phased arrays. These two categories of transducers are fundamentally different in terms of their functional and structural requirements.
One-dimensional phased array ultrasound transducers have been used in the field of medical imaging for several decades. A typical one-dimensional transducer is a flat, rectangular plate measuring approximately 12 mmxc3x9720 mm and holds a linear array of, for example, 64 piezoelectric elements set adjacent to one another. An ultrasound beam produced by the transducer is electronically focused in only an azimuth plane, and must be focused in an elevation plane by use of a lens.
In order to achieve the desired focus, the typical one-dimensional transducer uses a soft acoustic convex lens. Such a lens is made of a material that propagates sound at a slower velocity than that through the tissue of the patient, to achieve the focusing effect.
Two-dimensional phased array transducers are relatively new to the field of medical imaging. A typical two-dimensional transducer is configured with a flat array of piezoelectric elements in an x-y matrix. For example, an array of 3000 elements can be arranged in a matrix of 50xc3x9760 elements. An ultrasound beam produced by such a transducer is electronically steered and focused in both an azimuth plane and an elevation plane. In contrast with the one-dimensional transducer, the two-dimensional transducer does not require a lens for focusing the ultrasound beam.
FIG. 1 illustrates a partial two-dimensional phased array ultrasound transducer according to the prior art. A lead zirconate titanate (PZT) sensor 115 is mounted on a sensor support structure 110, which is enclosed within a transducer housing 105. Although this transducer does not require a lens for focusing, an environmental barrier (not shown) must be positioned on sensor 115 to prevent exposure of the sensor elements to acoustic gel and other environmental contaminants such as sterilants. The barrier also serves to protect a clinician and patient from electrical hazards caused by applied voltage to the transducer elements.
FIG. 2 illustrates an application of a prior art two-dimensional phased array ultrasound transducer. A two-dimensional phased array ultrasound transducer 205 includes a barrier 225. Transducer 205 transmits an ultrasonic signal through a patient""s rib cage 215, and receives and processes echo signals in order to produce an image of internal organ 220.
Since barrier 225 is not used for focusing, it is flat and has a uniform thickness. This construction introduces a problem. As transducer 205 is repositioned on the patient""s body 235, in an effort to obtain an optimum image of internal organ 220, the acoustic gel (not shown) that is used during the ultrasound procedure is forced out from between barrier 225 and the patient""s skin 230. An air gap 210 forms between barrier 225 and the patient""s skin 230. Ultrasound signals do not propagate well through air. Consequently, the desired image of internal organ 220 is not obtained.
Accordingly, there is a need for a two-dimensional phased array ultrasound transducer with an improved environmental barrier for maximizing contact with a patient""s body.
A two-dimensional phased array ultrasound transducer incorporating the present invention comprises a transducer housing, a sensor mounted within the housing, and a convex environmental barrier for placement against, and for maximizing contact with, a patient""s body. The environmental barrier does not necessarily provide any focusing capability, therefore the propagation velocity of sound through the environmental barrier is approximately equal to the propagation velocity of sound through tissue of the patient""s body.
The barrier can be manufactured of a material such as polyurethane, low-density polyethylene or a thermoplastic elastomer. Its contour can be a portion of an elliptical, parabolic, cylindrical or spherical surface.
The present invention reduces the opportunity for an air gap to develop between the environmental barrier and the patient""s body. Accordingly, the quality of an ultrasound image is improved.